An apparatus of this kind is known from German Pat. No. 857,852 which discloses two cylinders, guided coaxially with respect to each other, the outer cylinder supporting a piston rod guided together with the piston in the inner cylinder to which the comb element is threadedly connected. Manual relative displacement of the two cylinders generates the pressure which allows the hair-dyeing medium to enter through the comb element into the hollow tines. However, this requires the operator to manually perform two motions which are different from each other, namely on the one hand to guide the comb element in the correct manner through the hair tufts which are to be dyed and on the other hand to simultaneously feed the necessary amount of hair-dyeing medium into the comb element. Expert dyeing is not possible with such apparatus.
U.S. Pat. No. 2,603,233 discloses a hair-dyeing apparatus in which a housing, provided with a spring-biased piston and adapted to contain the hair-treatment liquid, must be set in rotation about its longitudinal axis by means of a handle and against the action of a torsion spring in order to open a stop valve by means of such rotation so that the liquid pressurized by the piston can be conveyed into a hollow comb member. The tines of the comb member participate in the rotation but the liquid cannot be conducted therethrough. Instead, the liquid passes through pads or other absorbent strips which are attached to the outside of the comb member. It is evidently the intention that rotation of the comb member will comb through the hair which is simultaneously wetted with the liquid by means of the pads. Such an awkward procedure is also unsuitable in practical operation.